Suction device for use in a papermaking machine and a papermaking machine using a suction device

ABSTRACT

The invention relates to a suction device ( 15 ) for use in a papermaking machine ( 1 ). The suction device ( 15 ) has a length (L) in the machine direction that extends from a first end ( 16 ) to a second end ( 17 ). The suction device ( 15 ) further has a surface ( 18 ) which, during use of the suction device ( 15 ) in the papermaking machine, will be facing a permeable fabric ( 4, 6 ) passing the suction device during operation such that this surface ( 18 ) is a fabric-facing surface ( 18 ). The fabric-facing surface ( 18 ) has a first part ( 19 ) which begins at the first end ( 16 ) of the suction device ( 15 ) and extends towards the second end ( 17 ) but ends before the second end ( 17 ) of the suction device. The first part ( 19 ) of the fabric-facing surface ( 18 ) is formed by a plurality of planar surfaces ( 23 ) which constitute end surfaces of a plurality of solid elements ( 21 ) and lie in the same plane such that, during operation, they can contact a fabric ( 4, 6 ) gliding over the fabric-facing surface ( 18 ) along a straight path. The solid elements ( 21 ) are separated from each other along the length of the suction device ( 15 ) such that channels ( 24 ) are defined between the solid elements ( 21 ), and the suction device ( 15 ) can be connected to at least one source of underpressure ( 26, 27 ) in such a way that the at least one source of underpressure ( 26, 27 ) is in communication with the channels ( 24 ) between the solid elements ( 21 ) such that, when the suction device ( 15 ) is used and the permeable fabric ( 4, 6 ) runs over the fabric-facing surface ( 18 ), the suction device ( 15 ) can act on the permeable fabric ( 4, 6 ) through the channels ( 24 ) and draw the permeable fabric ( 4, 6 ) towards the fabric-facing surface ( 18 ). The first part ( 19 ) of the fabric-facing surface ( 18 ) is followed by a second part ( 20 ) of the fabric-facing surface ( 18 ). The second part ( 20 ) of the fabric-facing surface ( 18 ) is a surface ( 33 ) formed as an end surface of a final solid element ( 22 ) which does not lie in the same plane as planar surfaces ( 23 ) belonging to the first part ( 19 ) of the fabric-facing surface ( 18 ) but is spaced from that plane such that, when the permeable fabric ( 4, 6 ) passes over the suction device ( 15 ), the permeable fabric ( 4, 6 ) will not contact the final solid element ( 22 ). The final solid element ( 22 ) is separated from a preceding solid element ( 21 ) such that a final channel ( 25 ) is defined between the final solid element ( 22 ) and the preceding solid element ( 21 ) and the final channel ( 25 ) being capable of communicating with at least one source of underpressure ( 26, 27 ) for the final channel ( 25 ). The invention also relates to a machine using the inventive suction device.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Nonprovisional applicationSer. No. 15/763,401, filed Mar. 26, 2018, which application is aNational Stage Application, filed under 35 U.S.C. § 371, ofInternational Application No. PCT/SE2015/051208, filed Nov. 12, 2015;the contents of all of which as are hereby incorporated by reference intheir entirety.

BACKGROUND Related Field

The present invention relates to a suction device for use in apapermaking machine. The suction device may be, for example, a mouldingbox intended for a through-air drying machine. The invention alsorelates to a papermaking machine that uses the inventive suction device.

Related Art

In papermaking machines, various kinds of suction devices are used thatact on fibrous webs through a fabric that is permeable to air and water.One use for such suction devices is as moulding boxes in through-airdrying machines, i.e. TAD machines. In a TAD machine, a wet fibrous webis dried as it is carried over one or several TAD cylinders on apermeable fabric with an imprinting pattern. To imprint athree-dimensional patterns into the fibrous web that is manufactured,the web and the permeable fabric can made to pass a moulding box beforethe web is carried by the permeable fabric to the TAD cylinder orcylinders. The moulding box is a suction device that draws the fibrousweb towards the permeable fabric as the web and the permeable fabricpasses the moulding box. This causes the wet fibrous web to be drawninto the permeable fabric such that the pattern of the permeable fabricis imprinted into the wet fibrous web. The pattern which has beenimprinted into the wet fibrous web will remain when the fibrous web hasbeen dried. An example of a moulding box is disclosed in, for example,U.S. Pat. No. 5,718,806.

The inventors of the present invention have noted that, in paper makingmachines using suction devices such as moulding boxes, there may bedisturbances in the area downstream of the suction device and that thismay sometimes be caused by the suction device itself. Therefore, it isan object of the present invention to provide an improved suction devicethat can be used, for example, as a moulding box in TAD machines.

BRIEF SUMMARY

The invention relates to a suction device for use in a papermakingmachine. The inventive suction device is suitable for acting on a wetfibrous web through a permeable fabric that runs through a part of thepapermaking machine. The suction device according to the invention has alength that extends from a first end to a second end which first end isan upstream end when the suction device is used in the papermakingmachine and which second end is a downstream end when the suction deviceis used in the papermaking machine and the direction from the first endto the second end is the machine direction when the suction device isused in the papermaking machine. The suction device further has a widthwhich is perpendicular to the length of the suction device and extendsin the cross-machine direction when the suction device is used in thepapermaking machine.

The inventive suction device further has a surface which, during use ofthe suction device in the papermaking machine, will be facing thepermeable fabric and thus be a fabric-facing surface. The fabric-facingsurface has a first part which begins at the first end of the suctiondevice and extends towards the second end but ends before the second endof the suction device. The first part of the fabric-facing surface isformed by a plurality of planar surfaces which planar surfacesconstitute end surfaces of a plurality of solid elements. The planarsurfaces of the solid elements in the first part of the fabric-facingsurface lie in the same plane such that, during operation, they cancontact a fabric gliding over the fabric-facing surface along a straightpath. The solid elements are separated from each other along the lengthof the suction device such that channels are defined between the solidelements and the suction device is configured to be connected to atleast one source of underpressure in such a way that the at least onesource of underpressure is in communication with the channels definedbetween the solid elements such that, when the suction device is usedand the permeable fabric runs over the fabric-facing surface, thesuction device can act on the permeable fabric through the channels anddraw the permeable fabric by suction effect towards the fabric-facingsurface.

The first part of the fabric-facing surface is followed by a second partof the fabric-facing surface which second part of the fabric-facingsurface is a surface formed as an end surface of a final solid elementand which end surface of the final solid element does not lie in thesame plane as planar surfaces of the solid elements belonging to thefirst part of the fabric-facing surface. Instead, it is spaced from theplane in which the planar surfaces of the solid elements belonging tothe first part of the fabric-facing surface lie such that, when thepermeable fabric passes over the suction device and moves past the finalsolid element along the plane of the planar surfaces of the solidelements belonging to the first part of the fabric-facing surface, thepermeable fabric will not contact the final solid element.

The final solid element is separated from a preceding solid element suchthat a final channel is defined between the final solid element and thepreceding solid element. The final channel is capable of communicatingwith at least one source of underpressure for the final channel when theat least one source of underpressure for the final channel is connectedto the suction device such that an underpressure can be generated in thearea between the permeable fabric and the surface of the final solidelement.

The solid elements are ribs that extend in a direction perpendicular tothe machine direction and the cross machine direction, i.e.perpendicular to the length and width dimension of the suction device.The ribs having ends at the fabric-facing surface which ends constitutethe surfaces of the solid elements.

In embodiments of the invention, at least the ends of the ribs thatconstitute surfaces of the solid elements in the first part of thefabric-facing surface are made of a ceramic material.

In embodiments of the invention, at least a part of the final channelformed between the ribs that constitute the final solid element and thesolid element immediately preceding the final solid element has asmaller cross-sectional area than the preceding channels. In suchembodiments, the final channel formed between the ribs that constitutethe final solid element and the solid element immediately preceding thefinal solid element may be provided with a flow restrictor.

In embodiments of the invention, the suction device is configured suchthat the channels defined between the solid elements of the first partof the fabric-facing surface can be connected to and communicate with atleast one first source of underpressure and that the final channel canbe connected to and communicate with at least one second source ofunderpressure which is separate from the at least one first source orunderpressure.

In some embodiments, the suction device may be formed as a single unit.

In other embodiments, the suction device may be formed by a first unitand a second unit which first and second units are physically separatefrom each other. In such embodiments, the first part of thefabric-facing surface can be formed on the first unit and the secondfabric-facing surface formed on the second unit.

In embodiments of the invention, the suction device may be configuredsuch that both the channels defined between the solid elements of thefirst part of the fabric-facing surface and the final channel all can beconnected to and communicate with at least one common source ofunderpressure.

The invention may also be defined in terms of a papermaking machine thatmakes use of the inventive suction device. Such a papermaking machinemay comprise a forming section and a drying section and the machinebeing will be arranged to cause a newly formed fibrous web to move alonga path of travel that extends in the machine direction from the formingsection to and into the drying section. The inventive papermakingmachine comprises an endless permeable fabric and a plurality of guiderolls around which the endless permeable fabric runs in a loop. Theendless permeable fabric is arranged to carry the fibrous web at least apart of the path of travel of the web and the inventive suction deviceis arranged inside the loop of the endless permeable fabric with thefabric-facing surface facing the endless permeable fabric.

The papermaking machine may be a machine that has a drying section thatcomprises a through-air-drying cylinder. The endless permeable fabricmay then be a through-air-drying fabric which is arranged to wrap a partof the through-air-drying cylinder and the inventive suction device isthen placed within the loop of the permeable fabric such that it can acton the permeable fabric and on a fibrous web that is carried by thepermeable fabric and separated from the suction device by the permeablefabric. The inventive suction device is then placed upstream of thethrough-air-drying cylinder such that it acts on the permeable fabricbefore the permeable fabric reaches the through-air-drying cylinder andthe fabric-facing surface of the suction device then has an orientationthat is more vertical than horizontal.

In other embodiments, the endless permeable fabric may be a formingfabric in the forming section and the fabric-facing surface of thesuction device may have an orientation that is horizontal or deviatesfrom a horizontal orientation by no more than 15°. In such embodiments,the fabric-facing surface of the suction device is facing downwards suchthat the permeable fabric passes below the suction device.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a side view that shows an example of a paper making machine inwhich the inventive suction device may be used.

FIG. 2 is a side view of another paper making machine in which theinventive suction device may be used.

FIG. 3 shows, in cross section, a view of an embodiment of the inventivesuction device in which the suction device acts against a permeablefabric on which a fibrous web is carried.

FIG. 4 is a view similar to that of FIG. 3 but in which the suctiondevice is shown without the permeable fabric and the fibrous web.

FIG. 5 shows a front view of the fabric-facing surface of the inventivesuction device.

FIG. 6 is a view similar to FIG. 3 but in which, for clarity, only thesolid elements are shown.

FIG. 7 is a view similar to FIG. 6 but in which an aspect of theinteraction with the permeable fabric and the fibrous web has beenadded.

FIG. 8 is a view similar to that of FIG. 7 but showing a differentembodiment.

FIG. 9 shows in greater detail the embodiment of FIG. 8 together withyet another optional feature.

FIG. 10 is a view similar to FIG. 3 but showing an alternativeembodiment.

FIG. 11 shows yet another embodiment of the invention.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

With reference to FIG. 1, a papermaking machine 1 is shown. Thepapermaking machine 1 of FIG. 1 is a machine intended for manufacturinga tissue paper web with high bulk such as, for example, TAD paper. Themachine may be intended for manufacturing tissue paper that has a basisweight that may be in the range of, for example, 12 g/m²-40 g/m² and mayinclude such grades as, for example, toilet paper or kitchen towel. Thepapermaking machine of FIG. 1 comprises a forming section 2 with a firstforming fabric 3 and a second forming fabric 4. The forming fabrics 3, 4may be, for example, foraminous forming wires that are air and waterpermeable. Each of the forming fabrics 3, 4 is arranged to run in a loopsupported by guide rolls 7. During operation, the forming fabrics 3, 4will run in the direction indicated by the arrows S. A head box 5 isarranged to inject stock in a gap between the forming fabrics 3, 4 as isknown in the art to which the invention pertains. The reference numeral34 indicates a forming roll. The forming section is followed by a dryingsection 8 that comprises a through-air-drying cylinder 9 (TAD cylinder9). From the second forming fabric 4, the newly formed fibrous web W istransferred to a subsequent permeable fabric 6.

In the embodiment of FIG. 1, the permeable fabric 6 is a through-airdrying fabric (TAD fabric) that is arranged to run in a loop supportedby guide rolls 7 in the direction of arrow S. A pick-up suction device14 may be arranged within the loop of the TAD fabric 6 to assist intransferring the fibrous web W from the forming fabric 4 to the TADfabric 6. The web W is then carried on the TAD fabric 6 around a part ofthe circumference of the through-air drying cylinder 9 (TAD cylinder 9).The TAD cylinder 9 is arranged in a hood 10. The hood 10 and the TADcylinder may be arranged to operate such that hot air passes from thehood 10, through the fibrous web W and the TAD fabric 6 and into the TADcylinder 9 and the air may then be evacuated from the TAD cylinder 9 inan axial direction. Embodiments are conceivable in which the hot airgoes the other way, i.e. from the inside of the TAD cylinder 9 and outthrough the TAD fabric 6 and the fibrous web W and into the hood 10. Thefibrous web W is dried as it passes the TAD cylinder 9 and is thenpassed further, for example to a reel-up. The reel-up is not shown inthe figures but, with reference to FIG. 1, it would normally be locatedto the left of the drying section 8. Such a reel-up could take manyforms and it may be, for example, such a reel-up as is disclosed in U.S.Pat. No. 5,901,918. The arrangement of the reel-up in relation to therest of the machine may be such that the reel-up is arranged to receivethe fibrous web from the drying section 8, for example from the TADfabric 6. The fibrous web may be sent from the drying section 8 in anopen draw to the reel-up or supported by something, for examplesupported by a fabric.

Embodiments are also conceivable in which the TAD cylinder 9 is followedby a Yankee drying cylinder (not shown) and in which the fibrous web issubsequently passed to a reel-up. Before the fibrous web W reaches theTAD cylinder 9, it passes a suction device 15 that is placed inside theloop of the permeable TAD fabric 6. At this stage, the fibrous web W mayhave a dryness of about 25% or perhaps even less and the web W caneasily be shaped. The suction device 15 may be a moulding box intendedto assist in creating a three-dimensional structure into the fibrous webW. As the fibrous web W passes the suction device 15, a suction effectfrom the suction device 15 pulls the fibrous web W against the TADfabric 6. As the TAD fabric 6 has a three-dimensional pattern withknuckles, fibers in the fibrous web W will be partially sucked into theTAD fabric such that the TAD fabric creates a three-dimensional patternin the surface of the fibrous web W, or at least into the side of thefibrous web that faces the TAD fabric. The suction device 15 plays animportant role in this process.

With reference to FIG. 2, a machine with a different layout is shown.The machine of FIG. 2 has a forming section 2 with a head box 5, a firstforming fabric 3 and a second forming fabric 4. The fabrics 3, 4 (bothof which are water and air permeable fabrics) run in the direction ofarrows S and they are supported in their loops by guide rolls 7. Thedrying section 8 comprises a drying cylinder 11 which may be a Yankeedrying cylinder 11. In operation, a newly formed fibrous web W travelson the lower side of the permeable fabric 4 (the fabric 4 may be a felt)to a nip N between a press roll 12 and the Yankee drying cylinder 11. Inthe nip N, the web W is transferred to the surface of the Yankee dryingcylinder 11. The surface of the Yankee drying cylinder 11 is smootherthan the surface of the fabric 4 which would typically be a felt. Sincethe surface of the Yankee drying cylinder is smoother than the surfaceof the fabric 4, the web W will follow the surface of the Yankee dryingcylinder 11 after the nip N. On the Yankee drying cylinder 11, the web Wis dried and subsequently creped from the surface of the Yankee dryingcylinder by a doctor 13.

In the machine shown in FIG. 2, a suction device 15 is placed inside theloop of the permeable fabric 4 and the suction device 15 may serve thepurpose of dewatering. It should be understood that other machineconfigurations are also possible and the suction device 15 may be placedinside the loop of a wire, for example in order to achieve additionaldewatering of the fibrous web.

A suction device acting on a fibrous web through a permeable fabric suchas, for example, a TAD fabric, typically has a number of slots oropenings through which underpressure can act. The underpressure (vacuum)sucks the fibrous web and the permeable fabric against the suctiondevice. The inventors have noted that in some applications using asuction device inside the loop of a permeable fabric, there may bedisturbances in the process downstream of the suction device. Theinventors have now identified the operation of the suction device as onesource of such disturbances. When a fibrous web carried on a permeablefabric passes a suction device, some fines and fibers will inevitably besucked through the permeable fabric and the inventors have found thatsuch fines and fibers tend to accumulate at a downstream end of thesuction device and clog the suction device at its downstream end. Atirregular intervals, pieces of wet fines and fibers may then fall of thesuction device and follow into subsequent parts of the process and causedisturbances. The present invention aims at eliminating or at leastreducing this problem such that disturbances of the papermaking processalso can be reduced.

One embodiment of the present invention will now be explained withreference to FIG. 3-FIG. 7. FIG. 3 shows a suction device 15 for use ina papermaking machine 1. The suction device 15 is suitable for acting ona wet fibrous web W through a permeable fabric 6 that runs through apart of the papermaking machine 1. The permeable fabric 6 may be a TADfabric which has a three-dimensional pattern that can be formed by, forexample, longitudinal yarns extending in the machine direction andtransverse yarns extending in the cross machine direction. Thethree-dimensional pattern may include knuckles and recessed portionssurrounding the knuckles. As best seen in FIG. 5, the suction device 15has a length L that extends from a first end 16 to a second end 17. Thefirst end 16 is an upstream end when the suction device 15 is used inthe papermaking machine 1 and the second end 17 is a downstream end whenthe suction device 15 is used in the papermaking machine 1. In FIG. 3,FIG. 4 and FIG. 5, the direction from the first end 16 to the second end17 is the machine direction MD when the suction device 15 is used in thepapermaking machine 1. As can be seen in FIG. 5, the suction device 15further has a width B which is perpendicular to the length L of thesuction device 15. The width B extends in the cross-machine direction(the CD direction) when the suction device 15 is used in the papermakingmachine 1.

With reference to FIG. 5 and FIG. 6, the suction device 15 has a surface18 which, during use of the suction device 15 in the papermakingmachine, will be facing the permeable fabric 4, 6 and thus be afabric-facing surface 18. As can be seen in FIG. 4, the fabric-facingsurface 18 has a first part 19 which begins at the first end 16 of thesuction device 15 and extends towards the second end 17 but ends beforethe second end 17 of the suction device. The first part 19 of thefabric-facing surface 18 is formed by planar surfaces 23 (see FIG. 6) ona plurality of solid elements 21 which planar surfaces 23 form a part ofthe fabric-facing surface 18. The planar surfaces 23 of the solidelements 21 in the first part 19 of the fabric-facing surface 18 lie inthe same plane such that, during operation, they can contact a fabric 4,6 that glides over the fabric-facing surface 18 along a straight path.The solid elements 21 are separated from each other along the length ofthe suction device 15 such that channels 24 are defined between thesolid elements 21. The spacing between the solid elements 21 may varyfrom case to case but in some embodiments contemplated by the inventors,the distance that separates the solid elements 21 from each other in themachine direction may be on the order of 15 mm-25 mm, for example 18 mm.The spacing between the solid elements 21 may be the same for all solidelements 21 but it may conceivably also vary.

The suction device 15 is configured to be connected to at least onesource of underpressure which is symbolically indicated as a fan 26 inFIG. 3 and FIG. 4. In this way, the at least one source of underpressure26 may communicate with the channels 24 defined between the solidelements 21 such that, when the suction device 15 is used and thepermeable fabric 6 runs over the fabric-facing surface 18, the suctiondevice 15 can act on the permeable fabric 6 through the channels 24 anddraw the permeable fabric 6 by suction effect towards the fabric-facingsurface 18. According to the present invention, the first part 19 of thefabric-facing surface 18 is followed by a second part 20 of thefabric-facing surface 18. The second part 20 of the fabric-facingsurface comprises a surface 33 (see FIG. 6) that does not lie in thesame plane as the planar surfaces 23 of the solid elements belonging tothe first part 19 of the fabric-facing surface 18 but is spaced from theplane in which the planar surfaces 23 of the solid elements 21 in thefirst part of the fabric-facing surface 18. It should be understood thatthe plane in which the surface 33 of the second part 20 of thefabric-facing surface 18 will normally be parallel or substantiallyparallel to the plane in which the planar surfaces 23 of the solidelements belonging to the first part of the fabric-facing surface 18 butthe two planes are separated from each other in a direction which isnormal to the two planes, i.e. perpendicular to the two planes. Thesurface 33 which does not lie in the same plane as the planar surfaces23 in the first part of the fabric-facing surface 18 is formed on afinal solid element 22 and can be seen as that end of the final solidelement 22 which, during operation, will be facing the permeable fabric6.

In FIG. 3, it can be seen how the plane in which the planar surface 33of the final solid element 22 lies is separated from the plane in whichthe planar surfaces 23 lie by a distance D. Therefore, when thepermeable fabric 6 passes over the suction device 15 and moves past thefinal solid element 22 along the plane of the planar surfaces 23 of thesolid elements 21 in the first part 19 of the fabric-facing surface 18,the permeable fabric 6 will not contact the final solid element 22. Theexact value of the distance D (see FIG. 3) depends on the circumstancesof each individual case but in some embodiments contemplated by theinventors, the distance D may be in the range of 3 mm-10 mm, for example5 mm or 7 mm but other values for the distance D are also conceivableand the distance D may conceivably be larger than 10 mm.

The final solid element 22 is separated from a preceding solid element21 such that a final channel 25 is defined between the final solidelement 22 and the preceding solid element 21. The final channel 25 iscapable of communicating with at least one source of underpressure forthe final channel 25 when the at least one source of underpressure forthe final channel 25 is connected to the suction device 15 such that anunderpressure can be generated in the area between the permeable fabric4, 6 and the surface of the final solid element 22. In the embodimentshown in FIG. 3 and FIG. 4, the source of underpressure 26 is the samefor both the final channel 25 and the preceding channels 24 butembodiments are conceivable in which this is not the case.

With reference to FIG. 3 and FIG. 4, it can be seen that the suctiondevice 15 may have a housing 36 that holds the solid elements 21, 22such that the solid elements 21, 22 are secured/fastened to the housing36 or in the housing 36.

With reference to FIG. 4 and FIG. 5, the solid elements 21, 22 can beunderstood as ribs that extend in a direction substantiallyperpendicular to the machine direction, i.e. in the cross machinedirection and that also have a certain extension in a directionperpendicular to the plane of the planar surfaces 23. The ribs have endsat the fabric-facing surface 18 which ends constitute the surfaces 23,33 of the solid elements 21, 22.

With reference to FIG. 9, the ends of some or all solid elements 21, 22may optionally (but not necessarily) be formed by a piece 28 of aceramic material such that one or several of the planar surfaces 23, 33may be formed on a ceramic material. In some embodiments, at least theends of the ribs that constitute surfaces of the solid elements 21 inthe first part of the fabric-facing surface 18 are made of a ceramicmaterial 28. The use of a ceramic material means that friction can bekept low and the resistance to wear is improved.

With reference to FIG. 8 and FIG. 9, it may be so in certain embodimentsthat at least a part 29 of the final channel 25 formed between the ribsthat constitute the final solid element 22 and the solid element 21immediately preceding the final solid element 22 has a smallercross-sectional area than the preceding channels 24. This can beachieved in several different ways. For example, the final channel 25formed between the ribs that constitute the final solid element 22 andthe solid element 21 immediately preceding the final solid element 22may be provided with a flow restrictor 30, for example a flow restrictorwhich, in cross section, is “pyramid-shaped” as shown in FIG. 9 butother shapes are also conceivable, for example rectangular shapes orflow restrictors 30 which, in cross section, have a curved shape.

With reference to FIG. 10, an embodiment is shown in which in which thesuction device 15 is configured such that the channels 24 definedbetween the solid elements associated with the first part 19 of thefabric-facing surface 18 can be connected to and communicate with atleast one first source of underpressure 26 and that the final channel 25can be connected to and communicate with at least one second source ofunderpressure 27 which is separate from the at least one first source orunderpressure 26. In FIG. 11, the first and second source ofunderpressure 26, 27 are symbolically shown as fans (and they mayconceivably be or comprise fans).

In embodiments of the invention, a common source of underpressure may beused while the air flow through the final channel 25 is regulated bymeans of a control valve (not shown in the figures).

The suction device 15 may be formed as a single unit but with referenceto FIG. 11, the suction device 15 may be formed by a first unit 31 and asecond unit 32. The first unit 31 and the second unit 32 are physicallyseparate from each other and the first part 19 of the fabric-facingsurface 18 is formed on the first unit 31 while the second part 20 ofthe fabric-facing surface 18 is formed on the second unit 32.

The function of the inventive suction device will now be explained withreference to FIG. 3, FIG. 7, FIG. 8 and FIG. 9. As can be seen in FIG. 3and FIG. 8, there is a gap A between the permeable fabric 6 and thesurface 33 of the final solid element 22. This is because the surface 33does not lie in the same plane as the planar surfaces 23 of the previoussolid elements 21. This allows air to flow between the fabric and thefinal solid element 22 as indicated by the arrow C in FIG. 7 and FIG. 9.The air flow through the final channel 25 will then catch fines, smallfibers and water droplets and draw them into the final channel 25thereby counteracting a build-up of large lumps of fines and fibers.Testing of the suction device has showed that, during operation, thefinal channel will quickly be blinded by fibers that lump together andact as a porous vacuum assisted wicket or gate. An effect of thisblinding is that the air flow required is reduced and no significantadditional vacuum capacity is required. The invention has been tested ona paper machine configuration where a suction device according to thepresent invention was used as a moulding box in a position upstream of aTAD cylinder (i.e. with a suction device 15 placed as shown in FIG. 1).The trials showed that the occurrence of breaks and defects wassignificantly reduced. Without wishing to be bound by theory, theinventors believe that the inventive form of the suction device has theeffect that fines and fibers that get blind the final channel aredewatered by the air flow and that, instead of falling off in largelumps, they fall off the suction device in the shape of individual finesor fibers that are substantially dry and that are individually too smallto cause any noticeable disturbances.

With reference to FIG. 9, it can be seen that the final solid element 22may have an extension 35 that is shaped as a triangle pointing in themachine direction. This extension 35 is optional and need not bepresent. When present, the extension 35 may serve to extend the lengthof the gap A. It may also serve to guide away condensated waterdroplets. The extension 35 (if present) may also be used simply for thepurpose of securing the final element 22 to the housing 36.

In embodiments where the final channel 25 has a part 29 with a smallercross-sectional area than the preceding channels 24, for example if ithas a flow restrictor 30, this entails the advantage that it will beeasier to achieve the effect that the final channel 25 gets blinded suchthat the required air flow is reduced.

In the configuration of FIG. 1, wet lumps of fines and fibers may falldownwards in a direction towards the through-air drying cylinder 9 ifthe suction device 15 is a conventional moulding box. However, when asuction device 15 according to the present invention is used, thisproblem can be at least significantly reduced.

In the configuration of FIG. 1, the suction device 15 is verticallyoriented or substantially vertically oriented. However, the inventivesuction device need not necessarily take the form of a moulding box in aTAD machine but could also be used in other places in a paper makingmachine, for example in such configurations in which the endlesspermeable fabric is a forming fabric 4 in the forming section. In suchcases, the fabric-facing surface 18 of the suction device 15 need not bevertically arranged but could have an orientation that is horizontal ordeviates from a horizontal orientation by no more than 15°. Thefabric-facing surface 18 of the suction device 15 is then facingdownwards such that the permeable fabric 4 passes below the suctiondevice 15. An example of such a configuration is shown in FIG. 2 where asuction device could be employed for additional water removal in theforming section but it should be understood that the configuration ofFIG. 2 is only an example since suction devices may be placed in ahorizontal or substantially horizontal position inside the loop ofpractically any permeable fabric in a paper making machine. Of course,it may also be placed in a vertical position for a number of reasons orin such a position that its orientation is somewhere between a verticalorientation and a horizontal orientation.

The invention may thus be understood also in terms of a papermakingmachine that makes use of the inventive suction device. The machineaccording to the invention comprises a forming section 2 and a dryingsection 8 and the machine is arranged to cause a newly formed fibrousweb W to move along a path of travel that extends in the machinedirection from the forming section 2 to and into the drying section 8.The papermaking machine 1 comprises an endless permeable fabric 4, 6 anda plurality of guide rolls 7 around which the endless permeable fabric4, 6 runs in a loop and the endless permeable fabric 4, 6 is arranged tocarry the fibrous web W at least a part of the path of travel of the webW and the papermaking machine 1 comprises a suction device 15 accordingto the invention and the suction device 15 is arranged inside the loopof the endless permeable fabric 4, 6 with the fabric-facing surface 18facing the endless permeable fabric.

In one embodiment of the inventive machine, the drying section comprisesa through-air-drying cylinder 9 and the endless permeable fabric 6 is athrough-air-drying fabric which is arranged to wrap a part of thethrough-air-drying cylinder 9 and the suction device 15 is placed withinthe loop of the permeable fabric 6 such that it can act on the permeablefabric 6 and on a fibrous web W carried by the permeable fabric 6 andseparated from the suction device 15 by the permeable fabric 6. Thesuction device 15 is then placed upstream of the through-air-dryingcylinder 9 such that it acts on the permeable fabric 6 before thepermeable fabric 6 reaches the through-air-drying cylinder 9, and thefabric-facing surface 18 of the suction device 15 has an orientationthat is more vertical than horizontal.

The surface 33 of the final solid element 22 may be planar just as theplanar surfaces 23 of the solid elements belonging to the first part 19of the fabric-facing surface 18 but it could also have another shape,for example a round shape. Since the final solid element 22 will notcontact the permeable fabric 4, 6, the final solid element 22 and thesurface 33 may very well be formed in a material such as High DensityPolyethylene (HDPE) which is less expensive and which can easily bemachined.

The inventive suction device is in particular useful as a moulding boxin a TAD machine (a Through Air Drying machine) for making through-driedtissue paper such as tissue paper having a basis weight in the range of,for example, 10 g/m²-30 g/m² but it could also be used as, for example,a transfer suction box in a tissue paper making machine or as adewatering element in, for example, the forming section of a tissuepaper making machine such as a TAD machine. While the inventive suctiondevice may be particularly useful in TAD machines, it may also be usedin other tissue machines than TAD machines, for example as a transfersuction box or dewatering element.

While the inventive suction device is in particular intended for tissuemachines (e.g. TAD machines), it may also be applied in machines forheavier grades than tissue.

It should also be understood that the invention may be defined in termsof a method of operating the inventive papermaking machine. In such amethod, the newly formed fibrous web would be caused to travel along apath of travel extending in the machine direction from the formingsection and to the drying section and thereby pass the inventive suctiondevice while at least one source of underpressure was connected to theinventive suction device and the source of underpressure is active(operated) to produce underpressure such that a suction effect throughthe suction device is generated and underpressure acts through thepermeable fabric on the fibrous web as the fibrous web passes theinventive suction device.

1. A suction device (15) for use in a papermaking machine (1) and beingsuitable for acting on a wet fibrous web (W) through a permeable fabric(4, 6) that runs through a part of the papermaking machine (1), thesuction device (15) comprising: a length (L) that extends from a firstend (16) to a second end (17) which first end (16) is an upstream endwhen the suction device (15) is used in the papermaking machine (1) andwhich second end (17) is a downstream end when the suction device (15)is used in the papermaking machine (1), the direction from the first end(16) to the second end (17) being the machine direction (MD) when thesuction device (15) is used in the papermaking machine (1), a width (B)which is perpendicular to the length (L) of the suction device (15) andextends in the cross-machine direction when the suction device (15) isused in the papermaking machine (1), a surface (18) which, during use ofthe suction device (15) in the papermaking machine, will be facing thepermeable fabric (4, 6) and thus be a fabric-facing surface (18), afirst part (19) which begins at the first end (16) of the suction device(15) and extends towards the second end (17) but ends before the secondend (17) of the suction device, the first part (19) of the fabric-facingsurface (18) being formed by a plurality of planar surfaces (23) whichplanar surfaces (23) constitute end surfaces of a plurality of solidelements (21), the planar surfaces (23) of the solid elements (21) inthe first part (19) of the fabric-facing surface (18) lying in the sameplane such that, during operation, they can contact a fabric (4, 6)gliding over the fabric-facing surface (18) along a straight path, thesolid elements (21) being separated from each other along the length ofthe suction device (15) such that channels (24) are defined between thesolid elements (21), and a second part (20) of the fabric-facing surface(18) following the first part (19), the second part (20) of thefabric-facing surface (18) being a surface (33) formed as an end surfaceof a final solid element (22) and which end surface (33) of the finalsolid element 22 does not lie in the same plane as planar surfaces (23)of the solid elements (21) belonging to the first part (19) of thefabric-facing surface (18) but is spaced from the plane in which theplanar surfaces (23) of the solid elements (2) belonging to the firstpart (19) of the fabric-facing surface (18) lie such that, when thepermeable fabric (4, 6) passes over the suction device (15) and movespast the final solid element (22) along the plane of the planar surfacesof the solid elements (21) belonging to the first part (19) of thefabric-facing surface (18), the permeable fabric (4, 6) will not contactthe final solid element (22), the final solid element (22) beingseparated from a preceding solid element (21) such that a final channel(25) is defined between the final solid element (22) and the precedingsolid element (21) wherein: the suction device (15) is configured to beconnected to at least one source of under-pressure (26, 27) in such away that the at least one source of under-pressure (26, 27) is incommunication with the channels (24) defined between the solid elements(21) such that, when the suction device (15) is used and the permeablefabric (4, 6) runs over the fabric-facing surface (18), the suctiondevice (15) can act on the permeable fabric (4, 6) through the channels(24) and draw the permeable fabric (4, 6) by suction effect towards thefabric-facing surface (18), and the final channel (25) is capable ofcommunicating with at least one source of under-pressure (26, 27) forthe final channel (25) when the at least one source of under-pressure(26, 27) for the final channel (25) is connected to the suction device(15) such that an under-pressure can be generated in the area betweenthe permeable fabric (4, 6) and the surface of the final solid element(22).
 2. A suction device (15) according to claim 1, wherein the solidelements (21, 22) are ribs that extend in a direction perpendicular tothe machine direction and the cross machine direction and to the lengthand width dimension of the suction device, the ribs having ends at thefabric-facing surface (18) which ends constitute the surfaces (23, 33)of the solid elements (21, 22).
 3. A suction device according to claim2, wherein at least the ends of the ribs that constitute surfaces of thesolid elements (21) in the first part of the fabric-facing surface (18)are made of a ceramic material (28).
 4. A suction device according toclaim 2, wherein at least a part (29) of the final channel (25) formedbetween the ribs that constitute the final solid element (22) and thesolid element (21) immediately preceding the final solid element (22)has a smaller cross-sectional area than the preceding channels (24). 5.A suction device (15) according to claim 2, wherein the final channel(25) formed between the ribs that constitute the final solid element(22) and the solid element (21) immediately preceding the final solidelement (22) is provided with a flow restrictor (30).
 6. A suctiondevice according to claim 1, wherein the suction device (15) isconfigured such that the channels (24) defined between the solidelements of the first part (19) of the fabric-facing surface (18) can beconnected to and communicate with at least one first source ofunder-pressure (26) and that the final channel (25) can be connected toand communicate with at least one second source of under-pressure (27)which is separate from the at least one first source or under-pressure(26).
 7. A suction device according to claim 6, wherein the suctiondevice (15) is defined by a first unit (31) and a second unit (32) whichfirst and second units (31, 32) are physically separate from each other,the first part of the fabric-facing surface (18) being defined on thefirst unit (31) and the second fabric-facing surface (18) being definedon the second unit (32).
 8. A suction device according to claim 6,wherein the suction device (15) is defined as a single unit.
 9. Asuction device according to claim 1, wherein the suction device (15) isconfigured such that both the channels (24) defined between the solidelements (21) of the first part (19) of the fabric-facing surface (18)and the final channel (25) are all connectable to and configured tocommunicate with at least one common source of under-pressure (26). 10.A papermaking machine comprising: a forming section (2), a dryingsection (8), an endless permeable fabric (4, 6) and a plurality of guiderolls (7) around which the endless permeable fabric (4, 6) runs in aloop, and a suction device (15), wherein: the machine is configured tocause a newly formed fibrous web (W) to move along a path of travel thatextends in the machine direction from the forming section (2) to andinto the drying section (8), the endless permeable fabric (4, 6) isconfigured to carry the fibrous web (W) at least a part of the path oftravel of the web (W), and the suction device (15) is arranged insidethe loop of the endless permeable fabric (4, 6) with the fabric-facingsurface (18) facing the endless permeable fabric.
 11. A papermakingmachine according to claim 10, wherein: the drying section comprises athrough-air-drying cylinder (9) and the endless permeable fabric (6) isa through-air-drying fabric which is arranged to wrap a part of thethrough-air-drying cylinder (9), and the suction device (15) is placedwithin the loop of the permeable fabric (6) such that it can act on thepermeable fabric (6) and on a fibrous web (W) carried by the permeablefabric (6) and separated from the suction device (15) by the permeablefabric (6), the suction device (15) being placed upstream of thethrough-air-drying cylinder (9) such that it acts on the permeablefabric (6) before the permeable fabric (6) reaches thethrough-air-drying cylinder (9), the fabric-facing surface (18) of thesuction device (15) having an orientation that is more vertical thanhorizontal.
 12. A papermaking machine according to claim 10, wherein:the endless permeable fabric (4) is a forming fabric (4) in the formingsection and the fabric-facing surface (18) of the suction device (15)has an orientation that is horizontal or deviates from a horizontalorientation by no more than 15°, and the fabric-facing surface (18) ofthe suction device (15) is facing downwards such that the permeablefabric (4) passes below the suction device (15).